FRANKFURT — Mario Draghi, president of the European Central Bank, warned Thursday that the structure of the euro zone had become “unsustainable” and criticized political leaders he said have been slow to respond to the sovereign debt crisis.

“The configuration we had for 10 years, which was considered sustainable, has been shown now to be unsustainable unless further steps are undertaken,” Mr. Draghi told a committee of the European Parliament in Brussels.

In what may have been his bluntest criticism of political leaders since taking office in November, Mr. Draghi said that half-measures and delays by political leaders have made the euro zone crisis worse. He said they need to decide what kind of euro zone they want.

“The next step is for our leaders to clarify what is the vision for a certain number of years from now,” he said. “The sooner this has been specified, the better. Dispel this fog.”